JP-A-2-264817 discloses a conventional rotation detecting device adopting a configuration, in which a magnetism detecting element composed of a hall IC, or the like, mounted on a circuit board, and a magnet are arranged on a substantially cylindrical-shaped resin casing, which comprises a detection surface for detection of a body being detected, in a manner to extend along the detection surface, and the circuit board, magnetism detecting element, and the magnet are sealed by a sealing material such as epoxy. In the case where the rotation detecting device is used as a rotation detecting device for a two-wheeler (for example, autobicycles), it is general that the rotation detecting device is mounted on a transmission casing, sprocket cover, or the like, of the vehicle and transmission gears, sprockets, or the like, rotating therein serve as a body being detected for detection.
In the case where such rotation detecting device is used to detect transmission gears, sprockets, or the like, as a body being detected, there is caused a problem that since the body being detected involves some clearances and so the body rigidity, displacement, or the like, of the vehicle (two-wheeler) causes vibrations on the body being detected, which varies a gap in a detection position associated with the body being detected and the rotation detecting device, changes in magnetism are generated in the rotation detecting device to make a detection noise, which leads to the cause of malfunctioning of, for example, an indicating instrument for indicating a speed, in accordance with output data, which are output from the rotation detecting device. Taking notice of such problem, the applicant of the present application has proposed a rotation detecting device, which is disclosed in JP-A-9-229714.
This rotation detecting device is adapted to be mounted on a front wheel (wheel) in a two-wheeler such as autobicycles, and constructed to comprise a housing provided with an insertion portion, through which an axle shaft mounting thereon the front wheel is inserted, the insertion portion having a plurality of magnetic poles for rotation with the front wheel, the rotation detecting device mounting thereon a body being detected, which body is made of a magnetic medium such as plastic magnet, and magnetism detecting means made of a hall IC, or the like, for detecting a change in the magnetic poles, caused by rotation of the body being detected.
With the body being detected, a cylindrical portion having the magnetic poles and rotation transmitting pieces for transmitting rotation of the front wheel to the cylindrical portion are formed integral by means of a plastic magnet, or the like. The rotation transmitting pieces are formed to extend outside of the cylindrical portion on an opening side of the housing so as to correspond to a recessed mount provided on a hub of the front wheel, the rotation transmitting pieces being provided in a plurality of locations on a peripheral edge of the cylindrical portion.
The rotation detecting device constructed in the above manner is arranged in a state, in which it is interposed between the front wheel and a front fork. More specifically, the rotation detecting device is arranged in a state, in which it is interposed between the front wheel and the front fork, by inserting the axle shaft, on which the front wheel is mounted, into the insertion portion, fitting the rotation transmitting pieces into the mount provided on the hub of the front wheel, and using nut members to fix the axle shaft, which projects outside the housing from the insertion portion, through the front fork.
When the rotation transmitting portion of the rotation detecting device is fitted into the mount of the hub in the manufacturing process of mounting such rotation detecting device to the hub, it is difficult to visually confirm whether the rotation transmitting pieces are fitted into the mount. Accordingly, there is caused a problem that there is a fear of breakage of the rotation transmitting pieces composed of the plastic magnet when the rotation detecting device is clamped between the hub and the front fork in an inappropriate state, in which the rotation transmitting pieces are not fitted into the mount.
The present invention takes notice of the problem and provides a rotation detecting device capable of being mounted to a hub of a wheel, without breakage of constituent parts of the rotation detecting device, even in the case where the rotation detecting device is arranged on the wheel in an inappropriate state.